You're right on track!
The mild headache may well be due to dehydration. We tend to come into sobriety already dehydrated from all the alcohol, and it takes a conscious effort to "catch up." My doc says that even a 10% dehydration makes all the organs work about 50% harder to do their jobs of detoxifying the body.
Walking has been one of the very important elements in my recovery also...it is my meditation.